1. Field
The present disclosure relates to a beam splitter for a 3D camera, and a 3D image acquisition apparatus such as a 3D camera, wherein the beam splitter is capable of separating a color image and a depth image, which are incident via a same incident surface, to proceed along different paths, and wherein the 3D image acquisition apparatus is capable of simultaneously capturing a color image and a depth image by using one lens and the beam splitter.
2. Description of the Related Art
Due to the development and increase in use of 3D display apparatuses, the development of 3D content has become important. Thus, research has been conducted into providing a 3D camera which allows a user to directly produce 3D content. A 3D camera may also be referred to as a RGBD image camera since it requires not only typical two-dimensional (2D) RGB color image information but also depth information (D).
The depth information is information about a distance between the 3D camera and surfaces of an object, and may be obtained by using a stereo vision method involving the use of two cameras, or by using a triangulation method involving structured light and a camera. However, according to the aforementioned methods, the accuracy of the distance information deteriorates as the distance between the 3D camera and the object becomes great. Also, it is difficult to obtain accurate distance information using the aforementioned methods because they are dependent upon a status of the surfaces of the object in question.
In order to solve this problem, a Time-of-Flight (TOF) technique has been introduced. The TOF technique irradiates a laser beam to an object, and then measures a travel time of the laser beam that is reflected from the object and is received by a light receiving unit. According to the TOF technique, light having a particular wavelength (e.g., near infrared rays having a wavelength of about 850 nm) is irradiated to the object by using a light emitting diode (LED) or a laser diode (LD), a light receiving unit receives the light that has the same wavelength and is reflected from the object, and a processing procedure is performed so as to extract depth information by modulating the received light using a modulator having a known gain wavelength. Various TOF techniques are available using various processing procedures.
A 3D camera used in conjunction with a TOF technique includes an optical system structure enabling it to simultaneously acquire a color image including general image information, and a depth image including depth information. For example, the 3D camera may respectively capture the color image and the depth image by using separate optical modules. However, in such a case, a mismatch may occur between the color image and the depth image due to a mismatch between an optical axis of an optical system used to obtain the color image, and an optical axis of an optical system used to obtain the depth image. Also, such a setup requires two object lenses in order to separately capture the color image and the depth image.
In this regard, in order to secure a match between a color image and a depth image and to simultaneously capture the color image and the depth image by using one object lens, an optical system structure in which a color image and a depth image may share one object lens is proposed. For example, in a color/depth image shared-type optical system, a color image and a depth image that are provided via a single object lens may be split by using a beam splitter, and the separate color image and depth image may be captured using separate image sensors, respectively. Thus, a/depth image shared-type optical system may have one object lens, one beam splitter, and two image sensors. A 3D camera employing this optical system structure may secure a match between two images, thereby acquiring a high-quality 3D image and achieving an excellent result with respect to form.
In order to extract distance information by using a TOF technique, it is necessary to arrange a modulator so as to modulate light that is reflected from the object. The modulator may be broadly classified as a reflection-type modulator or a transmittance-type modulator. Reflection-type modulators are more easily embodied are more frequently used. However, in a case in which a reflection-type modulator is used, a huge amount of light loss may occur in a beam splitter, and this light loss may decrease a signal-to-noise ratio (SNR) so that the light loss may deteriorate the accuracy of the depth information.